Social media advertising means business. Big business.

Already close to $5 billion last year, social ad spend is expected to increase year-on-year, rising to $6.1 billion in 2013, $8.4 billion in 2015 and a heady $11 billion by 2017.

Why? Primarily, the cost. Social ads are cheap. For the price of one Superbowl ad, a brand could run a Promoted Trend on Twitter every single day for three weeks. But why not do both? 71 percent of marketing agencies say that they run social media ads alongside their other online advertising campaigns, and more than one-third (34 percent) of marketers have generated leads through Twitter.

Reach, too, is greatly improved by social, particularly for local businesses – Twitter mobile users are 53 percent more likely to recall seeing an ad on Twitter than the average user. The (very nicely-designed) infographic below takes a closer look at the growth of social ad spend.

(Source: Salesforce.)